The present invention relates to a method for producing a solid-state imaging device having a photoelectric conversion portion including an organic film that generates electric charge in response to incident light. Particularly, the present invention relates to a method for producing a solid-state imaging device that can increase yield of the device.
As image sensors used for digital still cameras, digital video cameras, cameras for cellular phones, cameras for endoscopes, and the like, solid-state imaging devices (so-called CCD sensors and CMOS sensors), in which pixels having photodiodes are arranged on a semiconductor substrate such as a silicon (Si) chip, and signal electric charge corresponding to photoelectrons generated by the photodiode of each pixel is obtained by a CCD-type or CMOS-type readout circuit, are widely known.
In each pixel on the semiconductor substrate of these solid-state imaging devices, not only the photodiode but also a signal readout circuit and multilayer wiring subsidiary to the circuit are formed. Accordingly, as progress of pixel microfabrication is accelerated, the “decrease in aperture ratio,” as a phenomenon in which the readout circuit/wiring take up a relatively wide area and reduce a light-receiving area of the photodiode in one pixel, has become a problem. The decrease in aperture ratio leads to decrease in sensitivity.
Regarding the aforementioned problem, a laminate-type solid-state imaging device, which can increase the aperture ratio by forming a photoelectric conversion layer on top of a semiconductor substrate on which a readout circuit and wiring have been formed, is known. The laminate-type solid-state imaging device has configuration in which a large number of photoelectric conversion elements, which include pixel electrodes formed on a semiconductor substrate, a photoelectric conversion layer formed on the pixel electrodes, and a counter electrode formed on the photoelectric conversion layer, are arranged on a surface that is in parallel with the semiconductor substrate. In the photoelectric conversion element, when bias voltage is applied between the pixel electrodes and the counter electrode, an exciton generated inside the photoelectric conversion layer is dissociated into an electron and a hole, and a signal corresponding to the electric charge of the electron or hole that has moved to the pixel electrodes according to the bias voltage is obtained by a CCD-type or CMOS-type readout circuit disposed inside the semiconductor substrate.
In the laminate-type solid-state imaging device, pixel electrodes and an organic film which is formed by vapor-deposition of an organic material and functions as a photoelectric conversion layer are formed in the order mentioned on a semiconductor substrate in which a readout circuit has been formed. On the organic film, a counter electrode formed of a transparent electrode, such as ITO film, is formed. Moreover, a sealing film, a color filter, and the like are sequentially laminated on the counter electrode to produce the solid-state imaging device.
For example, as disclosed in JP 10-265940 A, the ITO film is formed by using a metal mask. Usually, the metal mask is fixed to a substrate by using a magnet. Therefore, the metal mask is formed by etching a plate made of a magnetic material.